There is currently a large research and development effort aimed at producing polymeric ion-exchange and ion-complexing materials (commonly known as ion-exchange materials) for a wide variety of applications. For the most part, these materials are resins comprising a cross-linked polymer (e.g., polystyrene crosslinked with divinylbenzene) that is substituted with an ion-exchange group either before or after polymerization. There are two major obstacles to the production of many different types of these resins with highly varied ion-exchange characteristics. First, the number of ion-exchange substituents that can be easily attached to reactive sites on the polymeric backbones of resins is limited. Secondly, only a limited number of polymers are available that exhibit suitable physical characteristics such as insolubility in water, resistance to abrasion, and resistance to osmotic swelling, and that also have chemically active sites for adding ion-exchange groups. For example, polytetrafluoethylene and polypropylene have such favorable physical characteristics but are chemically unreactive toward addition of ion-exchange groups.
There are many polymeric materials that exhibit desirable ion-exchange properties (e.g., high selectivity and high capacities to extract metal ions) but that are not structurally suited for use in ion-exchange processes. See, for example, J. Poly. Sci.: Polym. Let. Ed. 20(1982) 291 and J. Chem Soc. Dalton (1981)1486. Thus, it has been found that certain water-soluble polymers such as poly(vinylbenzocrownether)s and poly(vinylbenzoglyme)s are highly selective toward one metal ion over another, J. Pure Appl. Chem. 54(1982)2129. Other copolymers such as bicyclo[2.2.1]hept-5-ene-2,3-dicarboxylic anhydride with divinylbenzene and acrylic acid or acrylonitrile and p-vinylbenzoylacetone and acrylamide or maleic acid, all of which show poor abrasion resistance, are useful for separating Ca.sup.+2, Co.sup.+2, Cu.sup.+2 from other metal ions and for separating Cu.sup.+2 ions, Plaste Kautsch 29(1982)331, and for separating Cu.sup.+2 from other transition metal ions, J. Appl. Pol. Sci. 27(1982)811.
There is thus a substantial need to exploit the favorable ion-exchange characteristics of such materials by incorporating them into media with favorable physical characteristics. To this end, in U.S. Pat. Nos. 4,014,798, 4,045,352 and 4,187,333 there is disclosed hollow-fiber ion-exchange membranes comprising structurally sound porous hollow fibers containing a polymeric ion-exchange material within the fiber pores. However, because the ion-exchange material was not held firmly within the particular porous structure it was lost upon flushing the support with water.